Apparatus of this kind are widely known. They comprise a main body to which the wheel-alignment sensor is affixed at a predetermined reference direction to said main body. Three coplanar and substantially radial support arms are present on the main body, longitudinally adjusted spacers being mounted on the arms and the ends of which implement a three-point rest on the wheel rim being situated in a plane perpendicular to said relative direction. Means to keep the apparatus on the rim also are provided.
The wheel-alignment sensor held by such apparatus against a motor-vehicle wheel rim illustratively may be a spirit level and/or a laser sensor measuring a wheel's camber, track width, caster and the like.
In order to match the spacer to various rim diameters, it is known to fit the arms with elongated slots allowing clamping a spacer in various positions along the mounting arm to pass a tightening screw allowing clamping a spacer at various sites along the mounting arm. However this design incurs the drawback that because the support arms are fixed in their directions, the spacers cannot always be moved to come to rest between affixation screws of the vehicle wheel because, in different types of vehicles, these affixation screws are at different angular spacings, in other words, they will be present in different numbers. To allow measurement when there are different angular spacings, the state of the art has required keeping a supply of several affixation apparatus matched to different divisions, or numbers of, affixation screws.
U.S. Pat. 5,446,967 discloses an apparatus for fastening a wheel-alignment sensor to a wheel-rim of a motor vehicle which is based on a wholly different principle than the known ones cited above. In the apparatus of this U.S. patent, the arms are not support arms but adjusting rods mounted in radially displaceable manner in slots in the main body. Moreover the bases are not designed as spacers, rather they are affixation means to directly use one affixation screw or lug nut each for affixation to the wheel rim. It is critical for this known apparatus that there be four bases which must be screwed onto four affixation screws. The adjusting rods are radially tightened pairwise using opposite threads at a manually driven knurled disk, the main body is made symmetrical relative the wheel axis and furthermore inevitable play between the adjusting rods and the main body as well as between the adjusting rods and the bases pivotably affixed to them can be eliminated.